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Liner Lessons

by Anthony Howard, (M.ASCE), Civ. Engr.; Sewer Design Section, County Sanitation Districts of Los Angeles County, Whittier, CA,
Surendra Anketell, Supervising Engr.; Sewer Design Section, County Sanitation Districts of Los Angeles County, Whittier, CA,
Tommy Sung, (M.ASCE), Div. Engr.; Sewer Design Section, County Sanitation Districts of Los Angeles County, Whittier, CA,


Serial Information: Civil Engineering—ASCE, 2001, Vol. 71, Issue 10, Pg. 64,76


Document Type: Feature article

Abstract:

The County Sanitation Districts of Los Angeles County comprise 25 independent special districts that cover a service area of approximately 770 sq mi (1,990 km�). Since the early 1990s the consortium's ongoing sewer inspection program has identified approximately 135 mi (217 km) of deteriorated sewers, most of them large-diameter unlined concrete pipelines that have experienced significant hydrogen sulfide corrosion. The Districts have awarded more than 50 contracts to rehabilitate approximately 51 mi (82 km) of deteriorated sewers ranging in diameter from 8 to 109 in. (200 to 2,590 mm) at a construction cost in excess of $105 million. The primary rehabilitation methods have included slip-lining with centrifugally cast fiberglass-reinforced plastic mortar (CCFRPM), high-density polyethylene (HDPE), and polyvinyl chloride (PVC) segmented liner pipes; cured-in-place pipe (CIPP) liners; folded/re-formed PVC and deformed/re-formed HDPE pipe liners; the PVC pipe-lining system; and machine spiral-wound PVC pipe liners. Most of the rehabilitation work has involved slip-lining. The large-diameter sewers�those with a diameter greater than 48 in. (1,220 mm)�are most often rehabilitated by slip-lining with segmented plastic liner pipe, which is often the only alternative when flow cannot be removed from a sewer. CIPP liner has occasionally been used to rehabilitate large-diameter sewers, but a substantial number of imperfections have been observed in the installed liner, especially in curved sections. The PVC pipe-lining system, which requires human entry, has been used to rehabilitate curves and noncircular sections of some large-diameter sewers. Machine spiral-wound PVC pipe liner has not yet been installed in sewers of this size but has recently been included as an option to bidders. Medium-diameter sewers�between 27 and 42 in. (690 and 1,070 mm)�are most often rehabilitated by using CIPP liners or by slip-lining. Sewers 24 in. (610 mm) in diameter or smaller are most often rehabilitated by one of the various pipe-lining systems, which usually require flow diversion, bypass pumping, or both. For sewers less than 18 in. (460 mm) in diameter, deformed/re-formed HDPE and folded/re-formed PVC liners have been installed successfully. Machine spiral-wound PVC also can be installed as a radially expanding system for this size range with some flow in the sewer. Sewer rehabilitation is a continuously changing field as new products and systems become available and others are refined, and uniform specifications are often lacking. The development of uniform specifications adn information sharing are key factors in ensuring proper installation and long-term performance of the various rehabilitation methods.

Subject Headings: Plastic pipes | Sewers | Linings | Rehabilitation | Synthetic materials | Polyethylene | Construction equipment

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